From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from de01egw02.freescale.net (de01egw02.freescale.net [192.88.165.103]) by ozlabs.org (Postfix) with ESMTP id 86EBD67BAD for ; Tue, 24 Oct 2006 04:23:01 +1000 (EST) Message-ID: <453D0881.500@freescale.com> Date: Mon, 23 Oct 2006 13:22:57 -0500 From: Scott Wood MIME-Version: 1.0 To: Kumar Gala Subject: Re: [PATCH] qe_ic: Do a sync when masking interrupts. References: <20061019180308.GA24256@ld0162-tx32.am.freescale.net> <17724.15919.790114.628418@cargo.ozlabs.ibm.com> <453CDD70.9010100@freescale.com> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Cc: linuxppc-dev@ozlabs.org, Paul Mackerras List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Kumar Gala wrote: > > On Oct 23, 2006, at 10:19 AM, Scott Wood wrote: >> Possibly -- but the only problem on the rare occasions where the timing >> is not fortuitous is a spurious interrupt; the only reason the sync >> needs to be there at all is to avoid the overhead of the extra interrupt >> (and to avoid user complaints that they're getting "BAD" interrupts). > > > Why wouldn't the read accomplish the same thing in a more robust way > than the sync? It would. However, it also adds a small amount of overhead to every QE interrupt, and the only thing that that overhead buys is avoiding possible but empirically very rare spurious interrupts; it'd cost more than simply accepting that a spurious interrupt might happen once in a great while. Without any type of sync, spurious interrupts happen fairly regularly (about 5-10% of legitimate interrupts), so adding the sync should be a net gain over doing nothing. If the consensus is that a read should be done anyway, I can resumbit the patch that way; I just think it's overkill given that a 100% guarantee isn't required for correctness. -Scott